This year, 16 of Nigeria's 36 states have experienced cholera outbreaks. This has resulted in 1,622 suspected cases of the disease and 33 deaths. This is a steady increase in cholera cases after a remarkable sharp decline, from a total of 5,301 cases (186 deaths) in 2015 to 768 cases and 32 deaths in 2016

Lagos witnessed the last outbreak in October 2016 but in the last couple of weeks there have been outbreaks in Nigeria's Lagos, Kwara and Borno states.

Regional disparities in the death rates from cholera expose the different levels of emergency preparedness and health resources available. Understanding why this threat persists can help health authorities to reduce it, in Nigeria and elsewhere.

Cholera is an intestinal infection characterised by watery stool and diarrhoea. It is caused by the Vibrio cholerae, a bacterium, which releases toxins in the human intestine. This toxin activates excess secretion of water from the intestinal lumen that often lead to severe dehydration and sometimes death. Conditions that can lead to outbreaks include a disruption in water supply, poor basic sanitation and poor hygiene. Infected people show symptoms within two to five days. They can spread the disease even when they are not ill themselves by shedding the bacteria in their faeces.

As in other developing countries, cholera outbreaks occur mainly during the rainy season in Nigeria although they also sometimes occur in dry season. Flooding can cause septic tanks to contaminate surface water, especially open wells used for [drinking and food preparation]((http://www.water-research.net/index.php/bacteria). Contaminated flood water from the rains can also flow to vegetables and fruits which, if not properly washed, can cause an outbreak.

Cholera outbreaks happen when groups of people share infected water or food. When this happens, many people will require help at the same time. Health facilities and resources are often inadequate and ill-prepared to deal with such pressure.

The outbreaks in different parts of Nigeria are often driven by different factors. What they all point to, however, is that the country has not yet taken sufficient steps to address the "epidemiological triangle" that drives cholera outbreaks - host, agent and environmental factors. This includes early detection, better and stronger sanitation infrastructure that can withstand heavy rains as well as basic health infrastructure.

Lagos is the commercial centre of the country, with a densely settled population of over 20 million people. It lies along the coast and is prone to flooding. Despite the enormous efforts put into strengthening its primary health care system, it recorded 27 suspected cases of cholera and two deaths in July 2017. The outbreak has been attributed to heavy rainfall which eroded water sources, and to people getting help too late.

To reduce the number of outbreaks in the future, Lagos must tackle the factors that cause flooding. It must also take decisive steps to relocate residents from the most flood prone areas and improve on environmental sanitation and public health campaigns.

Borno State recorded the most serious outbreak of the three states. This northeastern state is the epicentre of the battle against the Islamic militant group Boko Haram. The outbreak affected the camp set up to accommodate people who had been displaced by the conflict. About 20,000 people are sheltered in this camp on the outskirts of Maiduguri, the Borno capital. The camp is overcrowded and lacks good amenities. People there are poorly nourished and don't have clean drinking water and sanitation.

Conflicts usually result in the destruction of infrastructure and disruption of services. This has worsened the situation in Borno, which already lagged behind other parts of Nigeria in social development. Health facilities are poorly equipped and staffed, and women in particular have low levels of education which usually means lower earnings, poor choices, slow reaction to illnesses and low problem solving abilities. These factors add to the risk of disease outbreaks and deaths.

Why cholera endures

It has been difficult to eradicate cholera because of the "epidemiological triangle" of host, agent and environmental factors.

Humans are the hosts. They carry and spread the disease. A person who has received treatment and is healthy again is still capable of spreading the infection to others. Vaccines are not very effective or long-lasting.

The environmental factors include poor access to clean, safe water and the lack of basic sanitation facilities.

To prevent and wipe out cholera, it's necessary to interrupt the host-agent-environment relationship. This can be achieved through more effective vaccines, improved host immunity, water chlorination and better ways of disposing of sanitary waste.

In poor countries, the lack of standard infection prevention and control in health facilities adds to the risk of diseases spreading. Health workers need to be continuously trained to detect, correctly diagnose and manage cases of cholera in a safe and effective manner.

Eradicating cholera and other diarrhoeal diseases in Nigeria will require a multi-sectoral approach. The ministries of water resources, rural development, urban planning and health must contribute, and government must show the political will to invest in infrastructure as well as health sector development.

Disclosure statement

Doyin Ogunyemi does not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond the academic appointment above.

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